1. Field of the Invention
The present invention relates to a vehicle control system for controlling running conditions, such as running speed and inter-vehicle distance, particularly for the purpose of avoiding a collision on the basis of the distance from or relative speed with respect to an object ahead of a vehicle.
2. Description of the Related Art
Conventionally, this type of vehicle control system is known as an Adaptive Cruise Control (ACC) that detects a preceding vehicle as an obstacle ahead of a vehicle, automatically controls the engine, gears, and brakes of the vehicle to provide a target acceleration that is determined on the basis of the distance from and relative speed with respect to the preceding vehicle, and the running condition of the vehicle. This makes it possible to properly maintain the distance from the preceding vehicle.
The ACC system typically has a limited maximum deceleration (minimum acceleration) that can be used in braking a vehicle for assuring safety of passengers. However, in some instances, even control at that maximum deceleration will not be able to avoid a collision with a preceding vehicle. For this reason, various control devices to be used in conjunction with an ACC system have been proposed for avoiding collision, including, for example, a device for signaling an alarm to a driver to prompt him or her, that is, to the person driving the vehicle, to intervene when it is determined that his or her vehicle is dangerously too close to a preceding vehicle (see Japanese Patent Laid-Open Publication No. 2000-177429); and a device adapted such that braking force generated when a driver intervenes and operates a brake is greater than a normal braking force for helping to avoid a collision (see Japanese Patent Laid-Open Publication No. Hei 11-139278). Further, other devices have also been proposed, which are not used with an ACC system, that detect a possibility of colliding with a preceding vehicle and automatically decrease vehicle speed by generating an acceleration (or deceleration) capable of avoiding the collision (see Japanese Patent Laid-Open Publication No. Hei 10-338110).
By combining these techniques, it will be possible to envision a control device for avoiding collision, which is used in conjunction with an ACC system, and which, when it is determined that a maximum deceleration of the ACC system is not sufficient to avoid a collision with a preceding vehicle, automatically decreases the vehicle speed by generating a deceleration (or negative acceleration) larger than the maximum deceleration.
However, using this type of device that automatically performs control for avoiding collision in addition to an ACC system, when a vehicle is in a potential collision state, the driver will not even be aware of this fact. Even if the driver is aware, the driver may not bother to intervene in the control, overestimating the effect of the device. These devices are merely for supporting drivers and, without the drivers' intervening in the control, will increase various risks all the more.
Specifically, these conventional control devices may not be able to avoid collision, even after performing any necessary control, depending upon the behavior of a preceding vehicle (e.g. abrupt deceleration) or the condition of the road surface (e.g. ice-covered road surface). Furthermore, if a sensor for detecting the preceding vehicle or obstacle makes a false detection, the control device will perform control for avoiding collision with something like an object on the street side that in fact poses no risk of collision, and will increase the risk of being rear-ended by a following vehicle.
In addition, ACC systems are mostly designed to suppress acceleration or deceleration if an object detected by a sensor is possibly not a vehicle, or if an object detected by a sensor is a vehicle but possibly is not correctly detected. In a case when the ACC system performs such suppression and at the same time a similar suppression is performed by an associated control device for avoiding a collision, it will not be possible to avoid collision with the detected object which is truly a vehicle.